I don't think anybody wants to keep doing that sort of whitelisting forever. It wouldn't surprise me to soon see an announcement from Google stating that they have decided on a date to end whitelisting and provide AAAA records to everybody. OTOH one way to put an end to whitelisting would be to only apply whitelisting to recursive resolvers that query the authoritative DNS servers over IPv4 and provide AAAA records to all that query over IPv6. Such an approach would be slightly problematic for Google since they don't have IPv6 support on their authoritative DNS servers, they don't have IPv6 support on their recursive resolvers either.

Apart from Google and Facebook is there any major site that uses whitelisting to decide who gets AAAA records? Is there actually any major site that provides AAAA records to all resolvers?

I only stumbled across Facebook white-listing because of an email that came across one of the IPv6 lists; they definitely don't market it like Google does.

Makes sense. Last I checked facebook wasn't fully functional if you only had IPv6 access. If you had dual stack and were using a resolver on the whitelist, some of the traffic would indeed go over IPv6, but there would still be some left on IPv4 and without that it didn't work. I don't know if that is still the case.